The present invention relates to optical computing devices and, more particularly, to optical design techniques that provide favorable fabrication characteristics for optical elements used in optical computing devices.
Optical computing devices, also commonly referred to as “opticoanalytical devices,” can be used to analyze and monitor a substance in real time. Such optical computing devices will often employ a processing element that optically interacts with the substance to determine quantitative and/or qualitative values of one or more physical or chemical properties of the substance. The processing element may be, for example, an integrated computational element (ICE), also known as a multivariate optical element (MOE), which is essentially an optical interference filter that can be designed to operate over a continuum of wavelengths in the electromagnetic spectrum from the UV to mid-infrared (MIR) ranges, or any sub-set of that region. Electromagnetic radiation that optically interacts with the ICE is changed so as to be readable by a detector, such that an output of the detector can be correlated to the physical or chemical property of the substance being analyzed.
One exemplary type of ICE includes a plurality of layers consisting of various materials whose index of refraction and size (e.g., thickness) may vary between each layer. An ICE design refers to the number and thickness of the respective layers of the ICE component. The layers may be strategically deposited and sized so as to selectively pass predetermined fractions of electromagnetic radiation at different wavelengths configured to substantially mimic a regression vector corresponding to a particular physical or chemical property of interest. Accordingly, an ICE design will exhibit a transmission function that is weighted with respect to wavelength. After the electromagnetic radiation from a light source interacts with a sample and ICE, the output light is conveyed to an optical transducer or detector. The total intensity measured by the detector is related to the physical or chemical property of interest for the substance.
It has been found, however, that the resulting transmission function for some ICE designs may change or shift based on errors in fabricating the individual ICE components. For example, during fabrication of an ICE component, slight errors may be made while depositing one or more of its layers. While some errors in a particular layer might cause a large shift in the transmission spectra of the ICE component as a whole, such errors may not be detrimental to the prediction performance of the ICE component. On the other hand, errors on another layer may cause only a slight spectral shift in the transmission profile, but this small shift may be significant with respect to prediction performance. It may be advantageous to determine which ICE designs may have hypersensitive layers for which extra care should be taken during the fabrication process to ensure minimal layer error.